Abstract: The ectomycorrhizal fungus Paxillus involutus was inoculated onto tissue-cultures of the hybrid poplar, Populus davidiana × P. bolleana, to evaluate the elemental defense effect to heavy metals copper and cadmium at different concentrations by simulating Alternaria alternata fungus infection. The enrichment capacity of Populus davidiana × P. bolleana for Cu and Cd was closely associated with the degree of heavy metal stress. There was a significant positive interaction of applying Cu and Cd and the inoculation with P. involutus on A. alternata leaf blight disease index. The incidence rate and disease index of leaf blight underwent a significant reduction compared with the controls. Similarly, the ratio of the area of disease spot to leaf area, incidence rate, and disease index for Populus davidiana × P. bolleana leaves inoculated with Paxillus involutus (Batsch) Fr. were significantly lower than those of their non-mycorrhizal counterparts. With increasing the degree of Cu and Cd stress, a gradual increase in the average value of the membership function for the incidence rate and disease index was observed, indicating the weakened pathogen’s ability to cause infection and the improved resistance of Populus davidiana × P. bolleana to leaf blight disease under Cu and Cd stress. Moreover, superoxide dismutase enzyme activity in Populus davidiana × P. bolleana increased significantly, reaching levels of 411.0 U/g FW and 421.6 U/g FW under Cu and Cd treatments, respectively. These changes in metabolic products and antioxidant enzyme activities suggest that P. involutus may enhance the resistance of Populus davidiana × P. bolleana to the fungus, Alternaria alternata Fr. Keissel under heavy metal stress by modulating these physiological indicators.

Key words: Populus davidiana × P. bolleana, Paxillus involutus, Alternaria alternate, Heavy metals, Elemental defense